woodchuckcanuck, I use left over Nova Seal to put over the top of my crates. It lasts much longer than the black tarps, more expensive of course too. 100' roll goes a long way though. https://www.buildings.com/product-c...uctid/1520/product/novaseal-roof-underlayment
I usually can get 2-3 years use for each piece. The tarps I use come off of the lumber bundles at the hardware stores. They give them away rather than see them go to landfill. Hard to beat free. I used them on the kiln for bldg wrap, and as a drop down tarp to redirect air flow. Quite sturdy.